The objective of this program is to develop improved techniques and applications of computerized tomography (CT) and further develop the MGH computerized tomography camera (MGH-CTC). Towards these ends, we propose to: a. Study fundamental aspects of radiation detection using high pressure xenon chambers. b. Develop the mechanical and electronic components of the MGH-CTC to improve precision, sensitivity and reliability. c. Develop algorithms for precise and quantitative reconstruction of CT images. d. Study physical aspects of CT scanners using phantoms to determine spatial and density resolution, effects of detector stability, radiation scatter, spectral effects and focal spot size. e. Investigate applications of CT in cancer diagnosis. f. Investigate applications of CT in cancer therapy.